Electrical igniter



Nov. 12, 1963 D. A. wEDwIcK 3,110,346

ELECTRICAL IGNITER Filed June '7, 1960 svs oazmnssaad FIG. 3

033:! BSGIELLHVO DON A. WEDWICK INVENTOR.

United States Patent Olice 3,ll,8b Patented Nov. l2, l

3,ll-,346 ELECTRCAL EGNTER Don A. Wedwieir, Mount Ariington, NJ.,assignor to Hercules Powder Company, Wilmington, Del., a corporation ofDelaware Filed .lune '7, 196i?. Ser. No. 34,419 4 Claims. (Si. 311-80)This invention relates to devices for iigniting thermally decomposablegas-generating charges. More specically, it is related to electricaligniters for igniting gas-generating charges in which the igniter isrepeatedly utilized.

The various types of electrical igniters heretofore utilized in theexplosives art have been of the perishable type. That is, for the mostpart, they have been one-shot devices which are usually destroyed orconsumed with the explosive that they were employed to initiate.However, with the advent of blasting methods which employ reutilizableapparatus such as pressure-resistant tubes and pressure-resistant drillsin conjunction with thermally de` composable gas-generating charges, therequirements of electrical igniters take on an entirely differentaspect. Such electrical igniters must then be re-utilizable, capable ofrepeatedly resisting extremely high pressures and ternperatures, andmust possess outstanding characteristics in respect to safety,reliability and longevity.

A primary object of the present invention is to provide devices meetingthe aforesaid requirements. Other objects of the invention will appearhereinafter, the novel features and combinations being set forth in theappended claims.

Generally described, the present invention comprises an electricaligniter for a gas-producing cartridge especially adapted for penetrationof the cartridge and repeated utilization having in combination supportmeans, a pair of spaced longitudinal conductive members, each of whichhas one end extending through the support means to form a pair ofelectrical terminals and each of which has the other end pointed andinwardly bent in close spaced relationship to each other, and heatingmeans bridging lthe conductive members near the inner point oftransition of the inwardly bent portion of each conductive member.

A preferred embodiment of the invention has been chosen for purposes ofillustration and description and is shown in the accompanying drawingwherein reference symbols refer to like parts Wherever they occur.

FIG. l is a part sectional, part elevational View of apparatus utilizingigniter means according to the invention.

FIG. 2 is an enlarged, fragmentary, part sectional, part elevationalview of igniter means constructed in accordance with the invention; and

PIG. 3 is a plan view of the igniter depicted in FIG. 2.

ln FIG. l, support members l, forming a part of an automatic blastingapparatus, are rigidly secured to a cylindrical combustion chamber 2having an aft or feed end for ingress of thermally decomposablecartridges containing gas-producing composition and a forward end ofreduced diameter for the egress of pressurized gas. Threadedly securedto the combustion chamber 2 is a retainer ring 3 which in turncompressively secures a head insert ring 4 between the ring 3 and thechamber 2 with an O ring-seal Zrs providing a gas-seal therebetween. Areciprocating ring head 5 slides into the head insert ring 4 and isgas-sealed by an O ring-seal Srs. The firing head 5 is provided with arigid, bifurcated electrical igniter 6 which is secured to the tiringhead by Ia retainer nut 7 which is threaded into the firing head. Acompression assembly is then provided by insulated washer S, socketconnector 9, and spacers it@ each side of Teflon seal l1. Thiscompression assembly with the seal l1 interposed between the spacers orrigid compression elements lil prevents any blow-back of high pressuregas through the ignition system since the retainer nut 7 is utilized toimpart considerable precompression on the assembly to insure that theTeflon seal is sufficiently tight about the lead wires and is firmlyseated to withstand the pressures generated in the combustion chamber.Although Teflon, which is a polytetrailuoroethylene resin, is preferredas the seal material, other resins and compressible sealing miaterialswhich are suitable for high temperature and high pressure service may beused. A compression spring l2 has one end secured to the retainer nut 7and its other end provided with a thrust washer i3. r[he spring in itsfully extended position extends to approximately the point of theigniter 6.

In operation of the device, it will be understood, of course, that thefiring head S and the assembly aiiixed thereto retract into an automaticfeed chamber (not shown) whereupon the points of the igniter 6 and thethrust washer 13 engage a cartridge 14 and push it forward to engage athrust seat l5, which in turn supports a shear ring lr6. The thrust seat15 is gas-sealed to the combustion chamber 2 by an 0 ring-seal 15m. Acartridge guide 17 affixed to the head insert ring 4- insures that thecartridge is guided to properly engage the shear ring 16. The cartridge14 comprises a paper shell 18, a heat-resistant rupturable closureelement 19 affixed to its fonvard end, a main gas-producing charge 2d, aprimer charge 2l, and a penetrable tinted end crimp 18e for closing itsaft or ignition end. When [the cartridge 14 is operatively positioned inthe combustion chamber 2, the rigid electrical igniter 6 has been forcedthrough the penetrable fluted end crimp lSc into the cant-ridge and haspenetrated the cartridge to a depth of about 11A inches. The firing head5 is then locked by suitable means (not shown) and the `device is readyfor firing. Electric firing current is then delivered via lead wires 22and 23 to the rigid electrical igniter `6 which ignites the ignition ofpriming charge 2l which in turn ignites the main gas-producing charge2t?. This results in a self-sustained decomposition of the cartridgeincluding its shell and when the resulting high pressure gases reach apredetermined pressure, the rupturable closure element l@ ruptures anddisintegrates with Sudden release of the gases from the combustionchamber 2 via a discharge orifice 24 to perform useful work,particularly in conjunction with blasting apparatus such as thatdisclosed in copending application of Robert W. Lawrence and Robert l'.Shiel, Serial No. 783,867, filed December 30, 1958 and now Patent No.3,055,648.

Referring to FIGS. 2 and 3, it rwill be noted that the igniter 6 is theigniter depicted in FIG. l which will now be described in detail. Theigniter 6 has a stainless steel support member Si). A pair of stainlesssteel spaced longitudinal conductive members 3l and 32, respeotiveiy,extends through the support member Sil. One end of each of thelongitudinal conductive members was threaded and utilized as a terminallas represented by 33 and 3d, respectively. insulating sleeves 35 and 36were provided through the support member 3i? to insulate the conductivemembers 3l and 32 therefrom. Flanges 3'7 and 3S integral with conductivemembers 3l and 32, respectively, |were provided to engage compatibleflanges on the insulating sleeves 35 and 36. A thick insulating member39 was provided within the support member 3@ with the conductive members3l `and 32 extending there* through. A nut and washer combination 4t)and el was provided with the nuts thereof engaging the threaded portions33 and 34, respectively, of conductive members 3l and 32. This assemblyprovided a rigid construction upon tightly securing the nuts whereuponthe insulating sleeves 35 and 36 and the insulating member 39 were Dprecompressed to form a seal resistant to high pressure gas as generatedon ythe ingress side of the igniter.

The ingress end of conductive members 31 and 32 was formed by pointingand inwardly bending each of the members as represented by 42 and 43,respectively, so that the ends thereof were in close spacedrelationship. Additionally, the facing surfaces 44 and 45 of conductivemembers 31 and 32, respectively, were finished to provide a parallelsurface. A heating element 46 was provided to bridge the conductivemembers 31 and 32 near the inner point of transition of the inwardlybent portion of each conductive member. The heating element extendedthrough the members and was finished flush with the outer surfacesthereof. The support member 30 was approximately 11/2 inches in diameterand l inch high. The conductive members 31 and 32 were eachapproximately 3A@ inch in diameter and extended from the support member30 about 4 inches to give a penetration of about 1% inches 'within thecartridge as heretofore described. The heating element 46 was made ofNichrome V, which consists of 80% nickel and 20% chromium, and had adiameter of about 0.040 inch and was positioned near the transitionpoint of the inwardly bent portion of the conductive members 3l and 32which was about 3A inch from the ends thereof. The spacing between theends of the conductive members 3'1 and 32 was about inch and theparallel facing surfaces 44 and 45 extended about 3716 inch.

With Ireference to the foregoing, it will be appreciated that althoughthe invention has been described with reference to stainless steel as apreferred material yfor the support member and the conductive members,other high temperature-resistant materials of construction may beutilized. For example, the support means may be made of nonconductivematerial :such as resins or ceramics whereby it is unnecessary toinsulate the conductive members therefrom. Similarly, although NichromeV is disclosed as a preferred material for the heating means, othernickel-chromium alloys and other resistance materials may be used.

With reference to the igniter heretofore described, it will beappreciated that the igniter is capable of penetrating hard cartridgecasings with hard interior substances as well as soft cartridge casingswith soft interior substances or any combination thereof. It will befurther appreciated that the igniter of this invention affords positiveignition when utilized with particulate or discrete packed explosivecharges since the design prevents the formation of hollows about theresistance element. Still further, although the invention has beendescribed in conjunction with automatic operation wherein thereciprocating ring head pushes the cartridge into the combustion chamberand is suitably locked without rotative movement, the igniter isparticularly adapted for rotative movement in conjunction with discretecharges wherein it is desired to use a rotative breech-lock or the like.

An example of operation of the invention is given for firing agas-generating device in accordance with the invention wherein thedevice in conjunction with the igniter of this invention is especiallyadapted and safe for coal mining as will be evident by the following. Aprimer charge essentially consisting of 42 grams of smokeless powdercomposition was packed into a llame-retardant paper container. Thecharge was ignited with a nonilaming initiator and did not ame in theatmosphere and would not ignite an explosive mixture of methane and air.The composition was as follows:

Nitroglycerin 15%. Nitrocellulose 20%. Nitroguanidine 51%. Celluloseacetate 7%.

Ethyl centralite 7%.

4 Calculated flame temp 2330 K. Particle size 0.053" diameter X 0.09"long.

The above composition also would not ignite or detonate when subjectedto impact from 30.06 or 0.22 caliber hollowpoint bullets, or #8 electricblasting caps, or 100- pound weight dropped from a height of 10 feet ona steel plate, or standard friction pendulum tests with steel shoe andanvil. Compositions of this type were then charged into cartridges asthe primer charge in conjunction with a main charge of the followingcomposition:

Percent Ammonium nitrate 49.0 Magnesium nitrate hexahydrate 34.0 Woodour 17.0

Main charge Weight grams 360 These cartridges were initated ashereinbefore described in a combustion chamber having a volume of 156cubic inches resulting in an average time of 4 seconds to rupture therupturable closure after application of current was applied to theigniter. The current applied averaged 24 amperes at l2 volts forapproximately 21/2 seconds. The average gas pressure generated was fromabout 8,000 to about 16,000 pounds per square inch which demonstratedthat the igniter of the present invention was suitable for use inconjunction with pressure-resistant tubes or pressure-resistant drillsor other cutting devices for the blasting of coal. Utilization of theinvention in actual mine tests verified the suitability demonstrated b'the above example.

From the foregoing, it is evident that there are several factors whichwill influence the choice of materials to be used in combination for themost satisfactory operation for the igniters of this invention. Forexample, the shell may be of any suitable material such as paper,plastic sheeting, cardboard or the like and should be nonflammable or bemade nonilammable by appropriate coating or other treatment. However,the shell should be thermally decomposable and substantially completelyconsumed during decomposition of the main charge wherein thedecomposition of the shell is essentially a combustion supported byoxygen from the main charge. The penetrable, nonconductive closure forthe shell may be the conventional uted crimp or the shotgun type crimp,or the like, and should be reasonably soft to accommodate penetration ofthe igniter. The fluted crimp is preferred since it is normally formedwith a small central opening permitting easy ingress of the igniter intothe cartridge. The cartridge should, of course, be moistureproof usingsuitable shell materials, coatings, or seals where necessary, inasmuchas ammonium nitrate which is the principal constituent of the maincharge is hygroscopic. The rupturable closure for the cartridge may bemade of any heatresistant, frangible material of desired strengthconsistent with the release of the pressurized gas at a pressureadequate for performing predetermined useful work such as the breakingof coal or other hard material. The shape of the rupturable end closureor shear disc may be varied considerably, the important thing being thatit serve to form a gas-tight seal for the combustion chamber duringgeneration of gas and thereafter rupture at a desired pressure. Apartial hemispherical shape is preferred as shown in the drawing sinceit readily disintegrates into small particles and is easily fabricatedand atiixed to the cartridge as by force-fitting, adhesive-sealing andthe like. The preferred materials of construction for the rupturableclosure are materials such as fiber or plastic which are nonsparking asthe disintegrated particles of the closure strike the vent openings of ablasting tube, blasting drill or other metallic implement utilized forthe high pressure work. It will be appreciated from the foregoing thatthe igniter or heating means of the invention is reciprocable andre-utilizable and should be sufficiently rigid to pierce the penetrableclosure and to penetrate the primer charge or the main charge, as thecase may be, within the cartridge.

The primer charges which may be used preferably contain a majorproportion o-f smokeless powder. As a permissible, such primers, ofcourse, should be nonlaming in the atmosphere and incapable of ignitingan explosive mixture of methane and air. Primer charges which have beenfound quite satisfactory for meeting the rigorous requirements of coalmining comprise from about 10 to about 20% of nitroglycerin, from about15 to about 25% of nitrocellulose, from about 50 to about 55% ofnitroguanidine or guanidine nitrate, from about to about of celluloseacetate and from about 5 to about 10% ethyl centralite or otherstabilizer, by weight, and conventionally colloided, extruded and cut tohave a particle size of from about 0.03 to about 0.10 inch diameter andfrom about 0.01 to about 0.10 inch long. Moderants such as cryolite,potassium sulfate, barium nitrate, potassium nitrate, and the like maybe added in small amount, not over about 1%, to the extent that they donot alter the principal characteristics of the primer composition whichare: nonllammable in the atmosphere; will not ignite explosive mixturesof methane and air; insensitive to standard sensitivity tests, such asrifle bullets, friction, blasting caps; and consistently and reliablycause main gas-generating charges to react under pressure. The quantityof primer charge utilized may be varied depending on the amount of themain charge, with from about 30 to about 70 grams usually found suitablefor use in conjunction with main charges used for blasting and similaroperations. The primer charge may be conveniently packaged in adecomposable plastic bag or the like prior to placing into the cartridgeor the primer and main charges may be placed in direct Contact with eachother. The calculated flame temperature for the primer compositioninsofar as permissibility is concerned may be Varied from about 1500o toabout 2500 K. It will be understood, of course, that in instances wherepermissibility is not a factor, other primers may be used in conjunctionwith the igniters of this invention and in instances where the maincharge is made sufficiently heat-sensitive and prolonged ignition timetolerated, the primer charge may be dispensed with entirely.

Compositions suitable for use as the main charge comprise ammoniumnitrate alone, desirably of relatively coarse granulation, or ammoniumnitrate, as the principal gas-generating constituent, that is, over 40%present, with other material such as the following typical composition:ammonium nitrate 49.0% magnesium nitrate hexahydrate 34.0%, carbonaceous(nut meal, pulp, starch) 17.0%; ammonium nitrate 75.0%, calciumcarbonate 25.0%; ammonium nitrate 90.0%, starch 10.0%; and ammoniumnitrate 65.0%, calcium formate 34.9%, calcium stearate 0.1.%

From the foregoing, it will be seen that the igniters in accordance withthis invention provide advantages heretofore not realized by the art inrespect to a high degree of safety, ease of operation particularly inrespect to semiautomatic and automatic operation, and economy.Furthermore, although the present invention has been described moreparticularly in respect to a combustion chamber suitable for utilizationwith automatic blasting apparatus, it may, of course, be utilized forother applications such as in conjunction with pressure-resistantblasting tubes, bolt-driving devices, catapult devices and the likewhere repeated tiring is desired for obtaining a source of very highpressure gas.

Still further, it will be seen that this invention may be carried out bythe use of various modiiications and changes Without departing from itsspirit and scope, with only such limitations placed thereon as imposedby the appended claims.

What I claim and ldesire to protect by Letters Patent is:

1. An electrical igniter which is designed to penetrate one end of agas-producing cartridge having a soft nonconductive container and toignite the cartridge for the production of high pressure gas in acombustion chamber, said igniter comprising in combination:

(a) a cylindrical supporting member,

(b) a pair of rigid longitudinal conductive members spaced from eachother and extending through the `supporting member to form a pair ofelectrical terrninals at one end thereof and inwardly bent toward eachother with their -facing surfaces in close parallel spaced relationshipat the other end thereof to form means for ease of pene-mation of theaforesaid cartridge,

(c) precompressed insulating and sealing means disposed within thesupporting member and surroundin-g the pair of electrical terminals toprevent the escape of aforesaid high pressure gas therethrough, and

(d) heating means bridging the conductive members and extendingtherethrough near the inner point of transition of their inwardly bentend portions whereby the aforesaid cartridge is ignited when the heatingmeans has penetrated -thereinto.

2. The electrical igniter as dened in claim 1 in which the support meansis nonconductive material.

3. The electrical igniter as `defined in claim 1 in which the supportmeans is conductive material and each of the conductive members isinsulated therefrom.

4. The electrical igniter as defined in claim 1 wherein theprecompressed insulating and sealing means comprises compressibleinsulating and sealing material interposed between rigid compressionelements.

References Cited in the tile of this patent UNITED STATES PATENTS1,361,689 Crousaz Dec. 7, 1920 2,064,706 Wiggert Dec. 15, 1936 2,370,159Hanley lFeb. 27, 1945 2,473,405 Zebree June 14, 1949 2,481,696 SeaveySept. 13, 1949 2,754,757 MacLeod July 17, 1956 2,767,655 Seavey Oct. 23,1956 2,882,820 Young Apr. 21, 1959 2,894,161 Sheheen July 7, 1959FOREIGN PATENTS 318,233 France Oct. 10, 1902

1. AN ELECTRICAL IGNITER WHICH IS DESIGNED TO PENETRATE ONE END OF AGAS-PRODUCING CARTRIDGE HAVING A SOFT NONCONDUCTIVE CONTAINER AND TOIGNITE THE CARTRIDGE FOR THE PRODUCTION OF HIGH PRESSURE GAS IN ACOMBUSTION CHAMBER, SAID IGNITER COMPRISING IN COMBINATION: (A) ACYLINDRICAL SUPPORTING MEMBER, (B) A PAIR OF RIGID LONGITUDINALCONDUCTIVE MEMBERS SPACED FROM EACH OTHER AND EXTENDING THROUGH THESUPPORTING MEMBER TO FORM A PAIR OF ELECTRICAL TERMINALS AT ONE ENDTHEREOF AND INWARDLY BENT TOWARD EACH OTHER WITH THEIR FACING SURFACESIN CLOSE PARALLEL SPACED RELATIONSHIP AT THE OTHER END THEREOF TO FORMMEANS FOR EASE OF PENETRATION OF THE AFORESAID CARTRIDGE, (C)PRECOMPRESSED INSULATING AND SEALING MEANS DISPOSED WITHIN THESUPPORTING MEMBER AND SURROUNDING THE PAIR OF ELECTRICAL TERMINALS TOPREVENT THE ESCAPE OF AFORESAID HIGH PRESSURE GAS THERETHROUGH, AND